Microstructural pore analysis of the catalyst layer in a polymer electrolyte membrane fuel cell: A combination of resin pore-filling and FIB/SEM

An analytical method was developed for focused ion beam (FIB)/scanning electron microscope (SEM) analysis of the microstructural pore properties of the catalyst layers in a polymer electrolyte membrane fuel cell (PEMFC). Generally, cross-sectional images of the catalyst layer obtained by FIB/SEM do not have uniform contrast in the pore area because carbons are often visible behind the cross-section, which makes conventional analysis inadequate. In the present study, by filling the pores of the catalyst layer with metalliferous epoxy polymer and using FIB/SEM, uniform contrast across the entire pore area was achieved without damage. The pore area was differentiated from the carbon network to produce a bi-segmented cross-sectional image. Subsequent digital image analysis revealed catalyst layer properties such as pore distribution and porosity at the microscopic level. The method was validated by comparing the porosity thus obtained from this method with that from mercury intrusion porosimetry measurements.